The present invention relates to a gear pump provided with a drive gear and a slave gear meshed with each other.
A gear pump is described, for example, in Japanese Patent Publication No. 15592/1991 (Hei 3-15592) wherein this conventional gear pump is, as shown in FIG. 1, provided with a drive gear B rotating via a drive shaft A; a slave gear C meshed with the drive gear B; a gear housing E provided with a gear chamber D containing these drive and slave gears B and C; and a pump housing G containing the gear housing E and functioning as a low pressurized chamber F the inside of which communicates with said gear chamber D.
The pump housing G is composed of a housing main body G1 defining an opening on one side of the housing in the axial direction of the drive shaft A and a detachable covering member G2 for closing the opening.
A gear pump as described above is arranged in such that accumulated in the above described low pressurized chamber F is an operating fluid such as oil, the operating fluid contained in the low pressurized chamber F is sucked into the gear chamber D to be a pressurized, the pressurized fluid is delivered to the outside of the pump housing G, and then the fluid is to be returned to the low pressurized chamber F as a return fluid from a fluid return port (not shown).
In the gear pump constituted as described above, return fluid is directly returned to the low pressurized chamber F. Since the return fluid is returned to the low pressurized chamber F at a certain velocity, there has been a problem that an operating fluid contained in the low pressurized chamber F is agitated by the return fluid and thus air bubbles produced by the agitation are sucked into the gear chamber D, resulting cavitation.
Furthermore, the problem of such cavitation may be solved by such an arrangement that a volume of the low pressurized chamber F is permitted to increase, thereby permitting the operating fluid in the low pressurized chamber F to make difficult to be agitated by the return fluid.
However, it results in such a problem that the pump housing G, in its turn, the overall gear pump becomes large-sized, on the other hand.